Integrated circuit die may be designed for stacking using TSVs. TSVs are vertical conductive paths formed between the bottom surface of the die and top surface of the die. TSVs may be formed in the die using conductive material, such as but not limited to copper. TSVs allow thousands or tens of thousands of vertical connections to be made between the dies in a stack. The advantage of stacking die using TSVs over older approaches, such as die stacking based on peripheral bond wire connections, is a greater number of higher speed interconnects may exist between die in a stack. Also the physical size of the die stack is reduced since the TSV connections are made between the bottom and top surfaces of the die, i.e. the die do not need a periphery connection area.
FIG. 1 illustrates a die 100 including various forms of TSVs 102-110. Each TSV forms a signaling path between the bottom surface 114 of the die and the top surface 112 of the die. The signals propagated on the paths may be analog or digital signals. As seen each TSV 102-110 is coupled to a contact point 118 on the bottom surface of the die and a contact point 116 on the top surface die. The contact points could be for example, but not limited too, a metal pad or a micro bump.
TSV 102 forms a non-buffered input and/or output (I/O) path between contact point 118 on the bottom surface 114 of the die and contact point 116 on the top surface 112 of the die. TSV 104 and buffer 120 form a buffered input (I) path from contact point 118 of the bottom surface 114 of the die to contact point 116 on the top surface 112 of the die. TSV 106 and buffer 122 form a buffered input (I) path from contact point 116 of the top surface 112 of the die to contact point 118 on the bottom top surface 114 of the die. TSV 108 and buffers 124 and 126 form a doubled buffered input (I) path from contact point 118 on the bottom surface 114 of the die to contact point 116 on the top surface 112 of the die. TSV 110 and buffers 128 and 130 form a doubled buffered input (I) path from contact point 116 on the top surface 112 of the die to contact point 118 on the bottom surface 114 of the die.
During the manufacture of Die 100, each TSV 102-110 path should be tested for connectivity to insure signals may be passed between contact points 118 on the bottom surface of the die and contact points 116 on the top surface of the die. If die 100 had ten thousand TSVs to test, a die tester would have to have the resources to test all ten thousand TSVS, which can be a very expensive proposition.
FIG. 2 illustrates an example of an upper die 100 stacked on top of a lower die 100. The die are connected via the TSV 102-110 contact points 116 on the top surface 112 of the lower die and the TSV 102-110 contact points 118 on the bottom surface 114 of the upper die. TSVs 102 of the lower and upper die form a non-buffered I/O path between the contact point 118 of the lower die and the contact point 116 of the upper die. TSVs 104 of the lower and upper die form a buffered input path from the contact point 118 of the lower die to the contact point 116 of the upper die. TSVs 106 of the lower and upper die form a buffered input path from the contact point 116 of the upper die to the contact point 118 of the lower die. TSVs 108 of the lower and upper die form a double buffered input path from the contact point 118 of the lower die to the contact point 116 of the upper die. TSVs 110 of the lower and upper die form a double buffered input path from the contact point 116 of the upper die to the contact point 118 of the lower die. While this example shows two die 100 being stacked, additional die 100 may also be included in the stack.
After stacking the Die 100, each stacked TSV 102-110 path should be tested for connectivity to insure signals may be passed between contact points 118 of the bottom surface of the lower die and contact points 116 on the top surface of the upper die. If the two die 100 had ten thousand TSVs to test, a stack die tester would have to have the resources to test all ten thousand TSVS, which can be a very expensive proposition.